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Building Wonders | Protecting Petra’s Future from Flash Floods

Examine an ancient dam network built to protect Petra’s “Treasury” monument from potentially damaging and deadly flash floods, in this video from NOVA: Building Wonders: Petra. A Swiss architect and archaeologist explains that clues in the landscape suggest that a reservoir, dug channels, and dams once worked together to spread out wintertime flood water that otherwise would have threatened the elaborate façade. The design was so perfect that today a team is repairing the dam network so it can once again protect this important ruin.

Cities rely on water to support the daily needs of their residents. But water is a scarce resource in desert climates, where rainfall is infrequent and total precipitation is little over the course of a year. While desert cities Las Vegas and Dubai receive close to 4 inches of precipitation each year, Cairo, Egypt, gets just an inch, and Lima, Peru, one-third of that. Compare these totals with cities in more moderate climate zones: Toronto receives about 30 inches of precipitation each year, and the Argentine capital of Buenos Aires gets close to 45 inches. Today, city water engineers develop water resource management strategies to meet residential and commercial needs. They may tap groundwater sources such as aquifers, construct large storage dams, and build wastewater treatment or desalinization plants. Two thousand years ago, the city of Petra, which received just 6 inches of rain annually, grew into a thriving center of trade in the arid climate of what is now southwest Jordan. Remarkably, Petra’s water engineers managed water resources without the benefit of computerized planning tools and heavy machinery. A nomadic people called the Nabataeans chose the location on which to establish an administrative, commercial, and religious center for strategic reasons. The site sits in a desert canyon, with natural cliff walls surrounding it. While the natural fortress would help protect the Nabataeans’ capital city, it brought challenges with respect to water supply and management. In ancient times, most people settled near proven freshwater sources to meet their basic needs for drinking, hygiene, and agriculture. Petra’s local streams could satisfy people’s needs. But the streams alone could not support a population that would swell to 20,000 or more.Archaeological evidence suggests that the Nabataeans developed sophisticated water technologies of their own to collect, store, and distribute freshwater. The Nabataeans demonstrated a strong grasp of hydraulics, or moving water under pressure. Their advanced understanding allowed them to create a system that ensured high flow rates and low leakage year-round. To bring water to the city center, they carved channels into canyon walls. For more remote sources, they employed clay pipelines, which were carefully planned to funnel the water along a continuous but gentle slope. They carved hundreds of cisterns, or underground storage tanks, from sandstone bedrock and lined them with waterproof mortar to prevent seepage. These covered enclosures, which protected the collected water from evaporation, supplied water to fountains, pools, bathhouses, vineyards, and orchards, even in times of drought.